1. Field of the Invention
The invention relates to a storage system, a copy method, and a primary storage apparatus. The invention is particularly suitable for use in a storage system including a storage apparatus where plural virtual volumes are paired.
2. Description of Related Art
A storage apparatus includes a controller for controlling data I/O to/from the storage apparatus and a disk device having plural hard disk drives for storing the data. A storage apparatus is an apparatus in which plural hard disks are managed in a RAID (Redundant Array of Independent/inexpensive Disks) format. At least one logical volume is formed in a physical storage area provided by a number of hard disks.
There is technology called remote copy, which is designed to avoid, by duplicating data in another storage apparatus located in a distant place, disaster-related loss of data, or similar, in such a storage apparatus.
Remote copy is technology for transferring data in a copy source storage apparatus (hereinafter referred to as a “primary storage apparatus”) to a copy destination storage apparatus (hereinafter referred to as a “secondary storage apparatus”) located in a distant place, and storing the data in a disk device in the secondary storage apparatus. A technique relating to remote copy is disclosed in Japanese Patent Laid-open Publication No. 11-85408, with which data is copied between different storage apparatuses not via a host computer. With the remote copy technology, data can be duplicated to avoid loss of data.
In recent years, Japanese Patent Laid-open Publication No. 2003-015915 has disclosed a technique in which no logical volume with a fixed capacity is created from a storage area in hard disks, but a virtual volume is provided using plural logical volumes. Storage areas in logical volumes are dynamically allocated to that virtual volume. With this configuration, storage areas that are in actuality dispersed over plural storage apparatuses can be provided as a single volume to a host computer.
Pairs of those virtual volumes are set and data is copied from a primary virtual volume to a secondary virtual volume, thereby maintaining data reliability.
If remote copy is executed utilizing the above described virtual volume technique on a storage system including primary and secondary storage apparatuses, all data (including zero data) in a primary virtual volume is copied to a secondary virtual volume when setting a pair so that the content of those virtual volumes are consistent.
However, in this method the amount of traffic is large, so data transfer takes a long time. Therefore, the load on the storage system accompanying data transfer is a problem.